It is conventionally known that microorganisms of the genus Bacillus , particularly Bacillus subtilis, produce Surfactin. The structure of Surfactin has been reported, for example, by Kakinuma et al. in Agric. Biol. Chem., 33, 971–972 (1969), Agric. Biol. Chem., 33, 973–976 (1969) and Agric. Biol. Chem., 33, 1523–1524 (1969).
Surfactin has an activity of decreasing the surface tension at a low concentration of 10 ppm or less and is easily biodegradable, therefore, the Surfactin has been taken notice of as an excellent surfactant. With respect to the process for producing Surfactin, the following methods are known. For example, K. Arima et al. disclose a method of producing Surfactin using a Bacillus subtilis strain ATCC 21331 or ATCC 21332 (see, U.S. Pat. No. 3,687,926 and Biochem. Bioph. Res. Commun., 31, 488–494 (1968)) and state that according to this method, from 0.05 to 0.1 g/L of Surfactin is accumulated in the culture medium by the culturing for 24 hours.
Since this productivity of Surfactin is low for the industrial use, a large number of inventors have made efforts to improve the productivity. Cooper et al. disclose a method of producing Surfactin while continuously removing foam generated during the culturing of Bacillus subtilis ATCC 21332 (see, Appl. Environ. Microbiol., 42, 408–412 (1981)). According to this method, the yield of Surfactin is from 0.7 to 0.8 g/L.
Sheppard et al. disclose a method of growing Bacillus subtilis in a culture medium containing hydrolyzed peat and thereby achieving a yield of 0.16 g/L (see, Appl. Microbiol. Biotechnol., 27, 110–116 (1987)). Mulligan et al. disclose a method for improving the yield of Surfactin by using a mutant strain of Bacillus subtilis ATCC 21332 (see, Appl. Microbiol. Biotech., 31, 486–489 (1989)). According to this method, the yield of Surfactin after culturing for 40 hours is 0.562 g/L.
Okuda et al. disclose a method for increasing the yield of Surfactin by culturing Bacillus subtilis in a magnetic field (see, JP-A-6–121668 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). Wei et al. disclose a method for increasing the yield of Surfactin by culturing Bacillus subtilis ATCC 21332 while adding an iron in a high concentration (see, Enz. Microbiol. Technol., 22, 724–728 (1998)), where the yield of Surfactin is 3.5 g/L.
Carrera et al. disclose that Bacillus subtilis ATCC 55033 as a mutant strain of Bacillus subtilis ATCC 21332 has an activity to produce Surfactin in a concentration of 2.0 to 4.0 g/L (see, Japanese Patent No. 3030789, U.S. Pat. No. 5,227,294). Kim et al. disclose that Surfactin is produced in a concentration of 7.0 g/L when Bacillus subtilis C9 is cultured under the conditions of oxygen limitation using glucose as a carbon source and NH4HCO3 as a nitrogen source (see, J. Ferment. Bioeng., 84, 41–46 (1997)).
These improvements are, however, not sufficient for the industrial use of Surfactin. A strain having a higher productivity and a production process for further elevating the productivity are being demanded.